Members of the Turkish-backed Free Syrian Army ride in a caravan in the city of Azez, near the Syria-Turkey border on January 19. File Photo by Hasan Kirmizitas/EPA-EFE

Dec. 12 (UPI) -- Turkish President Recep Tayyip Erdogan said Wednesday his military will soon launch a military operation against terror groups in Syria it says are backed by the United States.

Turkey, he said, will target Kurdistan Workers' Party (PKK) and People's Protection Unit (YPG) separatists -- but will not engage U.S. troops.

"We will launch an operation east of the Euphrates within a matter of days to save it from a separatist terrorist organization," Erdogan said at a Turkish defense summit in Ankara. "It is time to realize our decision to wipe out terror groups east of the Euphrates [River]."

Turkey has for years criticized the United States' support for the groups and said it's grown increasingly concerned about observation posts along Syria's border with Turkey.

"It is clear that the purpose of these U.S. observation posts is not to protect our country from terrorists but to protect terrorists from Turkey," Erdogan said. "These are branches of the PKK. The evidence is clear. Why are you working with them instead of with us?"

Erdogan said he doesn't want disagreements about Syria to damage the country's relationship with the United States in the future.

U.S. officials say the YPG is not a terrorist group, but Turkey insists it's an offshoot of the PKK -- which the United States does consider a terrorist group.

The two sides have been fighting since 2011, which is when Assad began cracking down on protesters.

As the war continued, millions of Syrian refugees left the country -- many ending up in Turkey, Lebanon, Egypt and Iraq. The United Nations refugee agency, though, said in a report this week as many as 250,000 of the refugees could return to Syria next year.

"As the situation in Syria improves, some of these refugees are making the journey home," said Amin Awad, director for the Middle East and North Africa's Office of the U.N. High Commissioner for Refugees.